Electrically heated diesel oxidation catalyst

ABSTRACT

An exhaust gas aftertreatment system ( 10 ) for a vehicle having an engine ( 14 ) includes a fluid passageway ( 20 ) extending from the engine to an ambient ( 18 ) for fluidly communicating exhaust gas (F). A diesel particulate filter ( 30 ) is disposed on the fluid passageway downstream of the engine ( 14 ). Disposed downstream of the engine ( 14 ) and upstream of the diesel particulate filter ( 30 ) is an electric diesel oxidation catalyst ( 24 ) having a substrate ( 34 ). A first electrode ( 40 ) and a second electrode ( 46 ) are attached to the electric diesel oxidation catalyst ( 24 ). The first electrode ( 40 ) selectively delivers current through the substrate ( 34 ) to the second electrode ( 46 ) to generate heat at the substrate ( 34 ).

BACKGROUND

Embodiments described herein relate to a system, method and device forheating exhaust gas. More specifically, embodiments described hereinrelate to a system, method and device for heating exhaust gas to createa regeneration event at a diesel particulate filter.

Exhaust gas aftertreatment systems in diesel vehicles are locateddownstream of the engine for treating exhaust gases emitted from theengine. The aftertreatment systems typically include a diesel oxidationcatalyst, and a diesel particulate filter. Particulate matter from theexhaust gas accumulates on the diesel particulate filter, and if leftunchecked, can create a back pressure in the aftertreatment system.

A regeneration event is the periodic oxidation of the collectedparticulate matter in the aftertreatment system during routine dieselengine operation. When the diesel particulate filter of the exhaustsystem experiences a build-up of particulate matter, the particulatematter is oxidized to “regenerate” the filter. Regeneration is typicallyinitiated by increasing engine load and activating a post-injection ofdiesel fuel into the exhaust stream. This post-injection providessufficient heat to oxidize the trapped particulate matter within thediesel particulate filter.

Exhaust gas is a relatively poor conductor of heat. As such, the loadingof the engine must be increased to provide a sufficiently heated exhaustgas to initiate the regeneration downstream at the diesel particulatefilter. During low speed and low load operation of the engine, theresulting exhaust gas may not have a sufficiently high temperature toinitiate the regeneration.

SUMMARY

An exhaust gas aftertreatment system for a vehicle having an engineincludes a fluid passageway extending from the engine to an ambient forfluidly communicating exhaust gas. A diesel particulate filter isdisposed on the fluid passageway downstream of the engine. Disposeddownstream of the engine and upstream of the diesel particulate filteris an electric diesel oxidation catalyst having a substrate. A firstelectrode and a second electrode are attached to the electric dieseloxidation catalyst. The first electrode selectively delivers currentthrough the catalyst substrate to the second electrode to generate heatat the catalyst substrate.

A method of regenerating an exhaust aftertreatment system of an enginehaving a diesel particulate filter includes the steps of providing afluid passageway from the engine to an ambient, providing a substrateupstream of the diesel particulate filter, and heating the substrateelectrically. The method of regeneration also includes the steps ofheating the exhaust gas flowing through the heated substrate, anddelivering the heated exhaust gas to the diesel particulate filter toinitiate regeneration.

An electric diesel oxidation catalyst for an exhaust aftertreatmentsystem of an engine includes a housing that substantially encloses asubstrate. The housing has an inlet and an outlet configured forpermitting a flow of exhaust gas through the housing. A first electrodeextends through the housing and is configured for providing an electriccurrent to the substrate. A second electrode extends from the housingand is configured for receiving the electric current from the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of an exhaust aftertreatment system having anelectric diesel oxidation catalyst located downstream of an engine.

FIG. 2 is a schematic indicating the direction of flow of exhaust gasthrough the electric diesel oxidation catalyst.

FIG. 3 is a section view of the electric diesel oxidation catalyst takenalong line A-A of FIG. 2.

DETAILED DESCRIPTION

Referring to FIGS. 1-3, an exhaust gas aftertreatment system isindicated generally at 10, and has an exhaust pipe assembly 12 extendingfrom an engine 14 to an outlet 16, such as the outlet to an ambient 18.The exhaust pipe assembly 12 forms a fluid passageway 20 for the flow ofexhaust gas F from the engine 14 to the ambient 18.

A first portion 22 of the exhaust pipe assembly 12 extends from theengine 14 to an electric diesel oxidation catalyst (EDOC) 24. A secondportion 26 of the exhaust pipe assembly 12 extends from the EDOC 24 to adiesel oxidation catalyst (DOC) 28, which is upstream of dieselparticulate filter (DPF) 30. A third portion 27 of the exhaust pipe 12assembly extends from the DPF 30 to the outlet 16. Other portions of theexhaust pipe may be disposed between various components on theaftertreatment system 10, such as between the engine 14 and an exhaustbrake 29, between the exhaust brake and the EDOC 24, or between the DOC28 and the DPF 30.

The DPF 30 is a filter constructed from a very high temperatureresistant material. The DPF 30 catches and holds particulate matterentrained within the exhaust gases discharged into the exhaustaftertreatment system 10. The DPF 30 is periodically regenerated tolimit increases in exhaust aftertreatment system 10 back pressure and tomaintain engine 14 efficiency.

The DOC 28 is a flow-through device that includes a substrate, typicallya ceramic or a metal covered with a catalyst. As the exhaust gases Fflow through the DOC 28, carbon monoxide, gaseous hydrocarbons andliquid hydrocarbon particles (unburned fuel and oil) are oxidized,thereby reducing emissions.

Upstream of the DPF 30 and the DOC 28 is the EDOC 24. The EDOC 24 has ahousing 32 that substantially encloses a substrate 34 having a structurethat permits the flow of exhaust gas F through the substrate and that isdistributed within the cross-section of the EDOC, for example agrid-shape, a swirl-shape, a honeycomb-shape, a circuitous-shape, amesh-shape, or any other shape. The substrate 34 is made of metal,however other highly conductive materials are possible.

The housing 32 may be generally cylindrical or have any other shape thatpermits the flow of exhaust gas F from an inlet 36 to an outlet 38 andthrough the substrate 34. The first portion 22 of the pipe assembly 12provides the fluid passageway 20 for the flow of exhaust gas F into theEDOC 24 at the inlet 36, and the second portion 26 of the pipe assemblyprovides the fluid passageway for the flow of exhaust gas F out of theEDOC at the outlet 38. The housing 32 of the EDOC 24 may be metal,however other materials are possible.

A first electrode 40 is electrically connected to a power source on thevehicle, such as the engine 14, with a first transmission wire 42. Thefirst electrode 40 extends through the housing of the EDOC 24, and mayextend generally the radius or generally half the width of the EDOC,however other lengths of extension into the EDOC are possible. The firstelectrode 40 contacts the substrate 34 generally at the cross-sectionalcenter C of the EDOC 24 and the substrate. An isolator sleeve 44 isdisposed about the first electrode 40 to prevent the contact of thefirst electrode with the housing 32 of the EDOC 24. The isolator sleeve44 co-extends with the first electrode 40 less than the entire length ofthe first electrode 40 so that a portion of the first electrode isexposed. When current is run to the first electrode 40, the current isisolated from the housing 32 and the current is directed to the generalcross-sectional center C of the EDOC 24.

A second electrode 46 extends from the housing 32 of the EDOC 24 and isalso electrically connected to the engine 14 with a second transmissionwire 48. While the second electrode 46 extends from the housing, it isalso possible that the second electrode 46 may contact the substrate 34.

The first electrode 40 does not contact the second electrode 46, butinstead the electrodes are spaced from each other and separated by thesubstrate 34 within the EDOC 24. The electrodes 40, 46 may also bespaced from each other a distance D along the length of the EDOC 24. Thefirst electrode 40 delivers current from the engine 14 through thesubstrate 34 to the second electrode 48. It is possible that theselective introduction of current into the EDOC 24 can be at theactivation of a user or an automatic activation, such as by an enginecontrol module.

When the current flows from the first electrode 40, through thesubstrate 34, and to the second electrode 48, heat is created at thesubstrate. When current is delivered to the general cross-sectionalcenter C of the substrate 34, the heat created is generally uniformacross the substrate 34. The exhaust gases F that flow through the EDOC24 are heated by the substrate 34 and the housing 32, and the heatedexhaust gases flow to the DOC 28 and to the DPF 30. At the DPF 30, theheated exhaust gases F provide sufficient heat to initiate regenerationof the DPF.

While the aftertreatment system 10 of FIG. 1 has the EDOC 24 locatedupstream of the DOC 28, it is possible that if the EDOC 24 achieves asufficient exhaust gas temperature, that the aftertreatment system mayinclude only the EDOC with no downstream DOC. Further, it is possiblethat more than one EDOC 24 can be used to increase the exhaust gastemperature.

By electrically heating the EDOC 24, the DPF 30 on the aftertreatmentsystem 10 can be regenerated without having to increase the loading onthe engine 14, which allows regeneration at low engine speed and lowengine loading.

1) An exhaust gas aftertreatment system for a vehicle having an engine,the aftertreatment system comprising: a fluid passageway extending fromthe engine to an ambient for fluidly communicating exhaust gas; a dieselparticulate filter disposed on the fluid passageway downstream of theengine; an electric diesel oxidation catalyst disposed downstream of theengine and upstream of the diesel particulate filter on the fluidpassageway, the electric diesel oxidation catalyst having a substrate;and a first electrode and a second electrode attached to the electricdiesel oxidation catalyst, the first electrode for selectivelydelivering current through the substrate to the second electrode togenerate heat at the substrate. 2) The aftertreatment system of claim 1further comprising a first transmission wire electrically connected tothe engine for providing electric current to the first electrode. 3) Theaftertreatment system of claim 2 further comprising a secondtransmission wire electrically connected to the engine for transmittingelectric current from the second electrode to the engine. 4) Theaftertreatment system of claim 1 wherein the electric diesel oxidationcatalyst includes a housing enclosing the substrate. 5) Theaftertreatment system of claim 4 further comprising an isolator disposedabout the first electrode to prevent the contact of the first electrodewith the housing. 6) The aftertreatment system of claim 1 wherein thesubstrate permits the flow of exhaust gas therethrough. 7) Theaftertreatment system of claim 1 wherein the first electrode extendsinto the electric diesel oxidation catalyst generally the radius of theelectric diesel oxidation catalyst. 8) The aftertreatment system ofclaim 1 wherein the first electrode and the second electrode are spacedfrom each other and separated by the substrate. 9) The aftertreatmentsystem of claim 1 further comprising a diesel oxidation catalystdisposed on the fluid passageway downstream of the electric dieseloxidation catalyst and upstream of the diesel particulate filter. 10) Amethod of regenerating an exhaust aftertreatment system of an enginehaving a diesel particulate filter, the method comprising: providing afluid passageway from the engine to an ambient; providing a substrateupstream of the diesel particulate filter on the fluid passageway;heating the substrate electrically; heating exhaust gas flowing throughthe heated substrate; and delivering the heated exhaust gas to thediesel particulate filter to initiate regeneration. 11) The method ofclaim 11 further comprising the step of contacting a first electrodewith the substrate. 12) The method of claim 12 further comprising thestep of connecting the first electrode to the engine with a firsttransmission wire. 13) The method of claim 12 further comprising thestep of contacting a second electrode with a housing that substantiallyencloses the substrate. 14) The method of claim 13 further comprisingthe step of connecting the second electrode to the engine with a secondtransmission wire. 15) The method of claim 14 further comprising thestep of providing electric current from the engine to the firstelectrode, through the substrate, to the second electrode, and back tothe engine. 16) An electric diesel oxidation catalyst for an exhaustaftertreatment system of an engine, the electric diesel oxidationcatalyst comprising: a housing substantially enclosing a substrate, thehousing having an inlet and an outlet configured for permitting a flowof exhaust gas through the housing; a first electrode extending throughthe housing configured for providing an electric current to thesubstrate; and a second electrode extending from the housing configuredfor receiving the electric current from the substrate. 17) The electricdiesel oxidation catalyst of claim 16 wherein the first electrodecontacts the substrate generally at the cross-sectional center of thesubstrate. 18) The electric diesel oxidation catalyst of claim 16wherein the first electrode and the second electrode are spaced fromeach other and separated by the substrate. 19) The electric dieseloxidation catalyst of claim 16 further comprising an isolator sleevedisposed around the first electrode. 20) The electric diesel oxidationcatalyst of claim 16 wherein the housing is generally cylindrical.